The diencephalon, also known as the interbrain, is one of the five main major sections of the brain. It works closely with the cerebrum (end brain) and together with it forms what is known as the forebrain. The diencephalon is in turn divided into five other structures, which perform a variety of functions.
What is the diencephalon?
The name diencephalon is already derived from its location in the brain. It is located in the center of the brain between the cerebrum and the brain stem. The midbrain adjoins it apexward. Within the diencephalon is the 3rd ventricle, a cavity filled with cerebrospinal fluid. Along with the terminal brain (telencephalon), the midbrain (mesencephalon), the hindbrain (metencephalon) and the afterbrain (myelencephalon), it is one of the five large main sections of the brain. It is functionally inseparable from the end brain. The diencephalon is responsible for the senses of sight, smell and hearing. Furthermore, it also contains the centers for surface sensibility, deep sensibility and mental sensibility. The diencephalon represents the switching point between the autonomic nervous system and the endocrine system.
Anatomy and structure
The diencephalon is located between the end brain and the brain stem. Together with the end brain, it forms what is known as the forebrain (prosencephalon). During embryonic brain development, a primary brain vesicle first gives rise to the prosencephalon, from which both the cerebrum and the diencephalon then form with the formation of two secondary brain vesicles. This fact already indicates the close functional affiliation of both brain areas. The brainstem, in turn, consists of the midbrain, bridge (pons), and medulla oblongata, or afterbrain, which is extended. The diencephalon is connected to the brainstem via the midbrain. The cerebellum, which is responsible for motor function, is not directly adjacent to the diencephalon, but forms fibrous connections to the thalamus via so-called efferents, as well as a diffuse neuronal network across the brainstem to the diencephalon as well. Thus, the diencephalon can act as a central switching point. For this purpose, it is divided into five structural centers, which in turn have different functions to perform. The structures of the diencephalon include the thalamus, hypothalamus, epithalamus with pineal gland, the subthalamus, and the metathalamus.
Function and tasks
The diencephalon performs many important functions of the autonomic nervous system. It is responsible for balancing the sympathetic and parasympathetic nervous systems. It also controls the biorhythm. This is always done in close cooperation with the cerebrum. As the central control center, the diencephalon relays signals from the brain stem to the end brain. The coordination of the various functions is possible through the interaction of the five different structural areas: thalamus, hypothalamus, epithalamus, subthalamus and metathalamus. The thalamus represents the largest part of the diencephalon. It in turn consists of many core areas, each of which is connected to the cerebral cortex. Via the core areas of the thalamus, information and signals from the body are transmitted to the cerebrum, where they are processed and transformed into conscious sensory impressions. This is why the diencephalon is also called the gateway to consciousness. Thus, both sensitive stimuli, such as touch or pain, and sensory stimuli, such as smelling, tasting, seeing or hearing, are processed. However, the thalamus also has a filtering function to separate important from unimportant stimuli. This is necessary to protect the body from stimulus overload. Another area of the diencephalon, the subthalamus, controls the gross motor function. For fine-tuning, the subthalamus is further divided into a motor function-promoting and a motor function-inhibiting area. The epithalamus includes, among other things, the pineal gland, which represents an intermediate position between the endocrine nervous system and the endocrine organ. The pineal gland produces the hormone melatonin and is responsible for the biorhythm of the organism. However, the epithalamus also has other important functions regarding olfactory and optical sensory impressions. The metathalamus influences the visual function and controls, among other things, the perception of objects. The hypothalamus performs particularly important functions. It functions as the control center of the autonomic nervous system.It regulates body temperature, blood pressure, food and fluid intake, sleep and sexual behavior. Due to the connection of the hypothalamus to the pituitary gland, it also controls the endocrine system of the organism. Therefore, the diencephalon also acts as a mediator between the autonomic nervous system and the endocrine system.
Diseases and disorders
Due to the variety of tasks performed by the diencephalon, its disruption may also result in various diseases. Consequences of diseases in the diencephalon include sleep disorders, disturbances of the biorhythm, diseases of the autonomic nervous system, and hormonal diseases. For example, damage to the thalamus results in the so-called thalamic syndrome. Symptoms of this syndrome are central pain and neurological deficits. There is paralysis of one side of the body, hypersensitivity to touch stimuli, numbness and sometimes an increase in reflexes. The cause here is often a stroke affecting the corresponding brain area. The hypothalamus in turn controls the hormone system via the pituitary gland. Diseases of the hypothalamus therefore often lead to disturbances in hormone production or regulation in the hormone system. Many hormone-related diseases have their starting point here. Either too many or too few hormones are produced. The respective disease is often named after the hormone concerned. Depending on which hormone is affected, sleep disturbances, disturbances of the water balance, growth disturbances, hyper- or hypofunction of the thyroid gland and even hormone-related prostate cancer can occur. However, many disorders or damage in the diencephalon are only partial aspects of much broader disease processes.
